SQUIRREL MONKEYS (SAIMIRI SCIUREUS) PERFORM SIMILARLY TO OTHER NEW WORLD MONKEYS AND PROSIMIANS ON A TOOL USE TASK

Two-choice tool tasks have been used to test tool comprehension in a number of tool-using and non-tool-using primate species. Though spontaneous tool use was recently documented in a captive group of squirrel monkeys, tool comprehension has not been further studied in the species. We present data from two tool-pulling choice tasks with squirrel monkeys. In Experiment 1, subjects (n=6) were presented with a choice between two wooden rakes (one baited, one unbaited) to obtain an out-of-reach reward. Five subjects spontaneously pulled the baited rake over the unbaited rake (criterion: choosing the baited rake in 17 trials over two consecutive 10-trial sessions; mean sessions to criterion=2.83, SD=2.04). The food likely enhanced the salience of the baited rake, and as the rake handles were inserted into the enclosure at the beginning of each trial, subjects could use a natural pulling motion to receive the reward. In Experiment 2, subjects (n=6) were presented with a choice between two canes, one effectively baited and one ineffectively baited. Subjects were required to reach outside of the enclosure to manipulate the tools and pull in the bait. On average, subjects required 9.67 sessions (SD=4.23) to reach criterion (two consecutive sessions choosing the effectively baited cane in 10 of 12 trials). Experiment 2 performance was comparable to learning curves previously reported for New World monkeys and prosimians on the same task.